Spinal canal stenosis is a disease of various symptoms that appear due to compression of nerve tissues such as nerve root or cauda equina, as a result of narrowing of spinal canal caused by the hypertrophic degeneration of spine or ligamentum flavum constituting spinal canal, or the projection of intervertebral disk. Depending upon the stenosed site, spinal canal stenosis is classified as cervical spinal canal stenosis, thoracic spinal canal stenosis, lumbar spinal canal stenosis, diffuse spinal canal stenosis, sacral stenosis, etc. Examples of the symptom thereof are lumbago, pain of lower limbs, numbness, etc. due to nerve compression. Especially in the case of cauda equina compression, symptoms of lumbago, pain in lower limbs, numbness, cataplectic feeling become severe during walking.
As a treating agent for lumbar spinal canal stenosis which is one of spinal canal stenosis, limaprost which is a derivative of prostaglandin E1 has been known and used for the improvement in subjective symptoms of lumbar spinal canal stenosis (such as pain or numbness of lower limbs) and in walking ability.
On the other hand, the present heterocyclic derivative (1) or a pharmaceutically acceptable salt thereof has already been reported to be useful for the treatment of pulmonary hypertension or obstructive arteriosclerosis as a PGI2 receptor agonist (see, for example, Patent Document 1).
Patent Document 1: Pamphlet of International Publication WO 02/088084